262 



THE EYE IN EVOLUTION 



Figs. 272 and 273. — The Ammocoete Eye (after Studnicka). 



Fig. 272. — The eye of the 8 mm. lar\a 

 of Pctromyzon, showing the optic 

 vesicle and the smaller lens vesicle 

 superficial to it. 



Fig. 273. — The eye of the 18 nun. 

 ammocoetes showing the lens vesicle 

 incor^jorated into the optic vesicle. 

 In the latter the outer pigmented 

 layer and the highly differentiated 

 inner layer with the projecting visual 

 cells are evident. 



chambers till ^\'\i\\ fibrillar material, the cornea is entirely cellular, 

 the retina becomes relatively differentiated but blood vessels and 

 mesodermal elements do not invade the vesicular eye (Mawas and 

 Magitot, 1912; Diicker, 1924) (Figs. 274 and 275). Meantime the eye 

 sinks beneath the skin to become separated from it by a considerable 

 thickness of tissue. 



The depth at which the vesicular eye lies at this stage beneath the skin 

 suggested to Hagcdoorn (1930) that the lens was derived from the retinal 



Fig. 274. — The Eye of the Ammoccetes. 



A\ a late stage. On top is the surface epithelium, underneath which lies 

 the ii'i^sodernaal skin. Underneath this is the scleral cornea. The lens is 

 fully ' vnied, as also are the anterior and vitreous chambers (a drawing from 

 Mawas i 



